With Russia making its first moves in an expected spring offensive, the U.S. and allies are scrambling to get enough ammunition to Ukraine to fight off what could prove to be a decisive assault -- and to launch an offensive of its own.
As much of the war has shifted to major artillery battles in the eastern part of the country and Ukraine burns through rounds at a high rate, the U.S. and allies have had to significantly boost production of critical ammunition.
But a key question is whether enough can be produced and delivered in time.
MORE: Russia-Ukraine live updates: White House says Russian attack 'brutalizing'Last month, NATO Secretary General Jens Stolenberg said, "The war in Ukraine is consuming an enormous amount of ammunition and depleting allied stockpiles. The current rate of Ukraine's ammunition expenditure is many times higher than our current rate of production. This puts our defense industries under strain. For example, the waiting time for large caliber ammunition has increased from 12 to 28 months."
Last week, Ukraine's defense minister, Oleksii Reznikov, told his E.U. counterparts, in a letter obtained by the Financial Times, that Kyiv needed 250,000 artillery shells a month. He also said that his forces were firing only about a fifth of the rounds he said they would ordinarily use.
Rob Lee, a senior fellow in the Foreign Policy Research Institute's Eurasia Program, tweeted, "The single most important thing the EU can do to support Ukraine is to produce more artillery rounds. More artillery rounds will give Ukraine a better chance at achieving a breakthrough in its future offensives and to reduce Russia's advantages in an attritional fight."
A top Pentagon official says it's both a short-term and long-term problem.
"What the Ukraine conflict showed is that, frankly, our defense industrial base was not at the level that we needed it to be to generate munitions," Colin Kahl, undersecretary of defense for policy, told American lawmakers last week.
"Those are going to matter a year from now, two years from now, three years from now, because even if the conflict in Ukraine dies down, and nobody can predict whether that will happen, Ukraine is going to need a military that can defend the territory it has clawed back," he said.
U.S. Army officials and manufacturing companies in the U.S say they are confident they can meet Ukraine's needs, despite it blowing through U.S supplies much faster than expected.
Asked on Wednesday whether the U.S. was caught off guard by how much ammunition aid Ukraine needed and whether it was playing catch-up, Assistant Secretary of the Army for Acquisition, Logistics and Technology Doug Bush, said, "I believe we are keeping up with the demand. No other country has done what the United States has done here, in terms of having the stocks in advance, having them in the right condition to provide for our ally, moving them there, and sustaining them."
Bush noted that while it is "appropriate for Americans to always ask questions about what we could have done better," he said he was personally "astounded" at what the Army has been able to accomplish.
Currently, a munitions plant in Scranton, Pennsylvania, has increased its production of artillery shells from 15,000 to 70,000 shells a month.
And Lockheed Martin, which makes the High Mobility Artillery Rocket Systems (HIMARS) the U.S. has sent to Ukraine, is doubling its production of the launchers from 48 to 96 per year, executives say.
Officials at the company's Camden, Arkansas, factory say they are confident they can keep up with the increased pace.
"We're in a place now where we can meet the capacity demand," Jay Price, vice president of precision fire at Lockheed Martin, told ABC News during a recent visit. "We won't have to work around the clock. We ebb and flow. We want to make all of our deliveries on time. So, if we have to work weekends or if we have to go [to] a second shift, we'll do that."
HIMARS have been credited as having an important role in Ukraine's defense against Russia. The truck-like mobile rocket launchers are able to set up, fire and relocate in a matter of minutes after launching as many as six rockets toward a target.
The launchers have been particularly effective in fighting Russia's offensive in the Donbas region of eastern Ukraine by allowing Ukrainian forces to strategically attack specific Russian supply and ammunition depots as far as fifty miles from the front lines, slowing their ability to make advances. The system was also crucial in forcing Russia to withdraw from Kherson.
A Ukrainian official who spoke with ABC News in February confirmed that Ukraine's ability to strike targets with high precision has been thanks to support provided by the U.S., which has so far sent 20 of its own HIMARS systems to Ukraine as part of some $29.3 billion in total security aid to date.
A $2 billion military package for Ukraine announced by the Pentagon on Feb. 24 also includes more Guided Multiple Launch Rocket System (GMLR) rockets that are fired from the HIMARS launcher.
The United States has also contracted to provide Ukraine with 20 additional newly built HIMARS that will be part of the ramped-up production at the factory in Camden.
On Friday, the administration announced another $400 million aid package that included additional ammunition for HIMARS, additional 155mm artillery rounds and more 105mm artillery rounds.
In Tallinn, Estonia, two weeks ago, Defense Secretary Lloyd Austin spoke of the importance of the continuing security assistance to Ukraine as it prepares for Russia's "upcoming offensive" in the spring.
"We're going to provide them all the support that we can possibly provide them so that they can have the best chance of being successful in the upcoming offensive," he said then.
Back at Lockheed Martin's plant in Camden, Dennis Truelove, a product manager retiring this week after nearly 42 years, said he deeply believes in the capability of HIMARS and what he described as its fundamental purpose.
"In Camden, Arkansas, our production workers produce a weapons system that is second to none anywhere in the world," Truelove told ABC News. "Somebody's son, somebody's daughter, somebody's grandson, nephew, niece -- lives depend on the decisions that our production workers make on a daily basis at our facilities."
ABC News' Benjamin Siegel and Tom Souffi Burridge contributed to this report.